1. Field of the Invention
The present invention relates generally to bone surgery and, more particularly, to a fixation system for drawing together into engaging relationship for healing mutually opposed fracture surfaces of a pair of bone fragments at a fractured site.
In instances in which fracture of a bone has occurred or in which surgical osteotomy, that is, a planned fracture, has been performed, it is necessary to join the fragments together in a semi-rigid fashion, to promote rapid healing and eventual union of the bone fragments. The term "semi-rigid" is intended to imply that if too much or too little relative motion between the fragments occurs, eventual mal or non union may result.
In the specific instance of the varus deformed tibia, or bow leggedness, high forces occur in the medial compartment of the knee, resulting in arthritis and pain. Surgical intervention to relieve the arthritic condition requires that a wedge of bone be removed from the tibia in the frontal plane just below the tibial subchondral plate. Once this wedge is removed, the proximal tibial fragment is collapsed upon the distal fragment and the two fragments are fixed with some type of hardware. In this manner, the bow is taken out of the tibia and a uniform load distribution in both departments of the knee results. This causes the arthritic condition in the medial compartment of the knee to abate, and the pain disappears.
2. Description of the Prior Art
The hardware classically employed to fix the fragments in the above described procedure varies depending upon the preference of the surgeon In many instances existing hardware is modified to address the special osteotomy case.
An accepted technique for many years used Steinmann pins and associated external compression clamps This technique is described at pp. 272 and 273 of Manual of Internal Fixation by M. E. Muller et al, published in 1970 by Springer-Verlag, New York - Heidelberg - Berlin.
Elongated fixation plates overlying the fracture site have also long been known as evidenced by the patents to Collison, U.S. Pat. No. 2,494,229 and to Markolf et al U.S. Pat. No. 3,741,205.
The coventry staple was designed for wedge osteotomy cases and consists of a metallic flat staple with two prongs. When driven into the collapsed osteotomy site, one prong engages the proximal fragment, and one the distal fragment. Several staples are generally used at spaced locations along the fracture site. While sometimes effective, the conventry staples tend not to compress the fragments together, but only prevent distraction of the collapsed osteotomy site. Further, the cross section of the pointed spikes is quite small. As a result, the spikes have a tendancy to tear out of the surrounding bone, which, over time, can lead to loosening of fixity and eventual non-union. An example of an improved surgical staple for joining bone fragments is the patent to Austin, U.S. Pat. No. 3,862,631.
In some cases, a series of cancellous bone screws are threaded into each fragment and surgical wire is wrapped around each screw to cinch down the fragments While this method of fixation often leads to eventual union, it also frequently occurs that the screws tend to cut out and fixity is lost.
Another known method of fixation is provided by means of a bone pin which traverses the fracture as disclosed by the patent to Ulrich, U.S. Pat. No. 4,135,506. While this technique may hold the bone fragments in proper alignment, it does not serve to compress the fragments so as to encourage healing.
In still other instances, elongated plates are provided which extend along and attach to the outer surface of the bone and overlie the fracture but include a component which is driven into at least one of the fragments. Such an arrangement is disclosed in the patents to Getscher et al, U.S. Pat. No. 3,824,995, to Richmond et al, U.S. Pat. No. 3,955,567, and to Streli, No. 4,565,193.
Still another concept used for bone fixation utilizes an elongated plate which extends along and attaches to the outer surface of the bone fragment but includes an element which traverses the fracture. Such a device is disclosed by the patent to Mason, U.S. Pat. No. 3,025,853. A significant drawback of this technique is the requirement for a large incision in order to implant the plate. This calls for a substantial surgical effort and results in a longer healing time and increased trauma to the patient.
In many instances involving all of the foregoing devices, the staples, pins, and plates did not present adequate surface area to the underlying bone resulting in "cut out" and resulting loss of fixity. Furthermore, often times they did not adequately hold the bone fragments together, or provide any way for the surgeon to adjust the amount of compressive force applied to a particular situation.
Recognizing the drawbacks of the various methods and constructions of fixation for unintended fractures as well as for resection osteotomy, an improved system of fixation has been developed which would preclude the associated complications of the known devices and techniques.